Transistorized deflection circuit with selective feedback



E. A. PASCHAL Nov. 3, 1964 TmmsIsToRIzEDV nEFLx-:CTION CIRCUIT WITHSELECTIVE FEEDBACK 2 Sheets-Sheet 1 Filed April 18, 1961 .N PNN $1 knl Jmy n Nov. 3, 1964 E. A. PAscHAL 3,155,873

TRANSISTORIZED DEFLECTION CIRCUIT WITH SELECTIVE FEEDBACK Filed April1e, 1961 2 sheets-sheet 2 mf/Wax fon/W4 ,KP/64414, 5V

QM 9J N- of?? -3614 ,477614214 United States Patent Gffiee Eddi PatentedNov. 3, i954 3,155,873 TRANSISTORZED DEFLECTIN Ci'RCUl'I WiTH SELECTHVEFEEDBACK Edwin A. Paschal, Anaheim, Caiii., assigner to Hughes AircraftCompany, Culver City, Calif., a corporation of Delaware Filed Apr. i8,1961i, Ser. No. 163,822 Claims. (Ci. SiS- 27) This invention relates toan apparatus for magnetically defiecting the electron beam of acathode-ray type tube at high speed and more particularly to anapparatus including a transistorized amplifier including a transistoroutput stage adapted to handle substantial currents with minimum powerdissipation.

In a typical deiiection apparatus, it is generally necessary thatcurrents flowing through the yoke winding for defiecting an electronbeam reach a quiescent state following a change in an interval of timeequal to 12 microseconds or less. This, in turn, necessitates that thecurrent be charged into the yoke winding in microseconds or less. Incircuits of this type a typical yoke winding characteristically hasinductances of the order of microhenries and requires of the order of 12amperes Afor full deiiection on a 70 cathode-ray tube. It a step inputsignal is employed, it may be shown that a voltage of the order of 36volts is required to charge l2 amperes into a 3G microhenry yoke windingin 10 microseconds. Thus, an output stage capable of handling l2 amperesand maintaining 36 volts across each yoke winding is necessary to meetthe aforementioned typical requirements by conventional techniques. Inaddition, it is necessary that the transistor of each output stage becapable of dissipating 12x36 or 432 watts which is a very difficultrequirement in that this energy is dissipated continuously except duringtransient periods of operation.

It is therefore an object of the present invention to provide animproved high-speed magnetic defiection system.

Another object of the present invention is to provide a magneticdeiiection system incorporating a transistor output stage with minimumpower dissipation therein.

Still another object of the present invention is to provide a magneticdeflection system incorporating a nondissipative auxiliary device toprovide peak transient energy requirements.

A further object of the present invention is to provide a defiectionsystem incorporating a transistor output stage adapted to apply highvoltage across the yoke windings during transient periods withoutrequiring comparable energy dissipation in the output transistors duringquiescent conditions.

A magnetic deflection apparatus in accordance with the present inventionincludes a paraphase input stage which excites a push-pull output stagethat includes a non-dissipative current source. In operation, an inputsignal for controlling the deflection is converted to a push-pull signalby the paraphase input stage and is, in turn, amplified by the push-pulloutput stage and used to control differential currents throughdouble-ended deflection yoke windings, each of which have one extremityreturned to ground through respective current sensing resistors. Currentfiow through the deflection yoke windings is sensed and fed back to theparaphase input stage in a degenerative manner thereby to provide a highdegree of stability and to insure the differential character of thecurrents through the detiection yoke windings. Further, the pushpulloutput stage is poled in a manner such that the deflection yoke windingbeing turned on has maximum current flow therethrough and is the morenegative of the two windings. Power dissipation in the transistors ofthe push-pull output stage is minimized by a floating source of currentwhich is clamped to the more negative of the two deflection yokewindings and connected to control the voltage applied to the outputtransistors thereby to provide power to the transistors only on demand,i.e., only during transient periods.

The above-*nentioned and other features and objects of this inventionand the manner of obtaining them will become more apparent by referenceto the following description taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 shows a partial schematic fio'w diagram of a preferred embodimentof the present invention; and

FIG. 2 illustrates a schematic circuit diagram of the apparatus of thepresent invention.

Referring now to FIG. 1 of the drawings, there is shown a schematicblock diagram of the apparatus of the present invention for drivingdouble-ended deiiection yoke windings 10, l2. The deflection yokewindings ld, 12 are driven by a transistor output amplifier i3 which isexcited by a paraphase signal amplifier 14 which, in turn, has inputsthat are connected to an input terminal and to ground through summingresistors 15, i6, respectively. The transistor output amplifier 13includes n-p-n type transistors 17, 18, which include bases 19, 2li,emitters 2l, 22 and collectors 23, 24, respectively. The bases 19,

210 of transistors 17, 13 are connected to the push-pull outputs ofparaphase signal amplifier lillI and are responsive to deection voltagesVo and -Vm respectively, which are out of phase and which result fromthe output currents of paraphase amplifier i4. The emitters 2i, 22, onthe other hand, are connected to a common junction 26 which, in turn,receives current from a constant current source 27. The collectors Z3,24 of transistors 17, 18 are connected to one extremity of thedefiection yoke windings iti, 12, respectively, and the remainingextremities thereof are connected through current sensing resistors 28,29, respectively, to ground. ln addition, feedback resistors 30, 31 areconnected from the junction intermediate the deflection yoke windings10, 12 and current sensing resistors 28, 29, respectively, to the inputsof the paraphase signal amplifier 14- in a manner to providedegenerative feedback and thus stabilize current iiow through thedeflection yoke windings 1t), 12. Lastly, a voltage on demand generator33 is responsive to the voltages appearing at the inputs of thedeflection yoke windings 1li, i2, i.e., at the collectors 23, 24 oftransistors 17, 13 and has an output connected through resistors 34, 35to the bases 19, 2t), respectively, of the transistors 17, i3. Theinputs to the voltage on demand generator 33 are connected to the inputsof a negative voltage sensing device 36 which develops an output voltageequal to the more negative voltage applied thereto. This more negativevoltage is, in turn, transposed through an emitter-follower amplifier 37to the resistors 34, 35.. The function of the voltage on demandgenerator 33 is to minimize the voltage drops across the transistors 17,1d during quiescent periods and, in particular, to maintain the voltagedrop from the collectors 23, 214 to the bases 19, 20, respectively, at aminimum during quiescent periods as will be hereinafter explained.

Referring now to FIG. 2 of the drawings wherein like referencecharacters designate like elements, there is shown a more detailedschematic circuit diagram of the apparatus of FIG. l. In particular,paraphase signal amplifier 1li includes p-n-p type transistors titl, e2which have bases 43, 44, emitters 45, 46 and collectors 47, 48,respectively. The emitters 45, 46 of transistors 40, 42 are connected toa common junction which, in turn, is connected through a resistor 5G toa terminal S2 which is maintained at a potential of the order of +15volts relative to ground. The bases 43, 44 are connected,respectransistor 18 to increase.

atenei/e tively, through the resistor to the input terminal to theparaphase amplifier 14 and through the resistor 16't0 ground. Inaddition, bases 43, 44 are also connected, respectively, to feedbackresistors 31, 30. Lastly, the collectors 47, "48 are connected to thebases 19, 20, respectively, of the output transistors 17,118.

Secondly, the negativervoltage sensing device 36 includes diodes 57, 58connected from the collectors 23,

424,respectively, 'of transistors-17, 18 through resistors 59, 68 to anoutput junction 62. The diodes S7, 58 are poled in a k'directionto allowconventional current flow awayfrom the output junction 62. The emitterfollower 37 includes a transistor63 having a collector64 connected to aterminal 65 maintained at a potential of the order of +15 volts relativeto ground, a base 66 connected directly to the output junction 62 ofnegative voltage sensing device 36 and, in addition, connected through aresistor- 69 to the terminal 65, and an emitter V67 connected through aconstant voltage dropping network 68 t0 an output terminal 70. Theconstant voltage. dropping network 68 includes, for example, a capacitor71 and a Zener diode 72 connected in parallel from emitter 67 to outputterminal'7t) with the Zener diode 72 poled asv shown in the drawing. Theoutput terminal 79 of emitter-follower 37 constitutes the output of thevoltage on demand generator 33 (FIG. 1) which, as previously specified,is connected through resistors 34, 35 kto the bases 19, 20,respectively, of transistors'17, 18. In addition, emitter follower 37includes an n-p-n type transistor`74 having a collector 75 connectedtothe output terminal 70, an emitter 76 connected through a resistor 78toa terminal`79, the terminal 79 being maintained at apotential of theorder of -36 volts relative to ground,

and a base 77. A resistort) and a capacitor S1 are con- 91 toa'terminalV 92 maintained at a potential of the order of -6 voltsrelative to ground, A resistor 93 and a capacitor 94 are connected inparallel from terminal 92 to the base 88 of transistor 86.

A diode 96 is connected from the terminal 79 to-the junction Y26andpoled in a manner to preventltheipotential appearing at junction 26 fromgoing more negative than the potential maintained atterminal 79. Lastly,re-

sistors'199, 100 are connected across the deliection yokes 10, 12,respectively, for damping the voltage transients developed thereacross.

In order to explain the operation of the device of the vpresentinvention, a step-voltage waveform 101 will be applied to the inputterminal 54 of the paraphase ampliher v14 which, in turn, generates astep-down waveform -102 at the collector 47 of transistor 40 and astep-up waveform 103 similar to waveform '101 at the collector 48 oftransistor 42. The step waveforms 182, 103 are applied to the bases 19,20, respectively, whereby a decrease inpotential at the base 19causesthe tiow -of current through .transistor 17 to decrease and anincrease in voltage at the base causes the flow of current through Thedecrease in the flow of current through transistor 17 produces acorrespondingly less negative voltage yat they ungrounded extremityresistor 28, which positive-going excursion in voltage-is fed backthrough feedback resistor to the base 44 of transistor 42 thereby tocounteract the current of voltage waveform 103. The increase in currentthrough transistor 18, on the other hand, results in a greater voltagedrop across the voltage dropping resistor 29. This negafeedback resistor31 to the base 43 of transistor `4tlwhere it combines degenerativelywith the waveform 101. Thus, the connections from deflection yokewindings 10, 12 through feedback resistors 30, 31 to the bases 44, 43,respectively, of transistors-42, t6-are degenerative in character.

Referring now to the voltage sensing device 36 the resistor 69 and theresistors 59, 60 and diodes 57, '58 form a voltage dividingfnetwork fromthe terminal maintained at 15 volts relative to ground to the .inputside of the yoke windingsltl, 12. LWhen the input side of one of theyoke windings 12, as in the present case, experiences a negative-goingexcursion which exceeds the voltage drop across the resistor 59 anddiode 57 connected to the remaining yoke winding, the junction 62becomes negative relative to the input side of yoke 18, wherebysubstantially no current iiows throughfthe diode 57. Thus, junction62along with base 66 of transistor 63 follows the input side of deflectionyoke 12 negative by substantially a constant amount equal to the voltagedrop across lthe resistor 60 and the diode 58. The decrease in thepotential of base 66 of transistor 63 produces a corresponding'decreasein thepotential of emitter 67 which lowers the constant voltageidroppingnetwork 68 which, in turn, lowers the lpotential at `the output junction70 of the emitter follower 37. The transistor 74 functions so as toprovide current for the Zener diode 72 of the constant voltage network68 and, in addition, provides an appropriate negative potential at theoutput junction 70 should this be required to enable Athe base 66 oftransistor 63 to follow the 1negative excursion appearing at theinput-of deflection yoke winding 12. Thus, a voltage is developed atoutput junction 70 which is substantially constant relative `to thatdeveloped at the output junction 62 of voltage sensingdevice 36. Also,during quiescent conditions the potential developed at output junction7i) is substantially constant relative to the potentials of thecollectors 23, 24 of transistors 17, 18. This voltage available atoutput junction 7d is applied throughV resistors 34,3510

the bases 19, 2t) of transistors 17, 18 thereby to'apply thissubstantially constant voltage drop across the transistor 17 or 18 whichhas the more negative voltage at the collector thereof. The currentrequired by transistors 17 and 18 to generate the necessary currentthrough deiiection yoke windings 19 or V12 is provided by the largeinductor 84 and capacitor-85, which current is replenished by thetransistor 86. When the voltage at the output 7) of emitter follower 37makes a negative excursion, an increased voltage ldrop is applied acrossthe large inductor 84 thus causing additional current to liow. In orderto avoid damage tothe transistors 17, l18 by allowing too much currentto flow therethrough, a diode 96 is connected from junction 26 toterminal 79 and poled in a manner toprevent-junc- Ation 26 fromexperiencing excursionsrrnore negative than the potential appearing atterminal 79.

Although the Vinvention has been shown in connection with a certainspecific embodiment, it'will'befreadily apparent to those skilled in theart that various changes in form and arrangement ofl parts maybe made tosuit requirements without departing from the spirit and scope of theinvention.

What is claimed is:

1. An apparatus for magnetically deiiecting the electron beamk of acathode-ray vtype tube, said apparatus comprising lirst and lseconddeflection yoke windings each having tirst and second terminals, saidsecond terminals thereof being returned to a common junction maintainedat ground potential; first and second transistors of like conductivitytypes responsive to push-pull deflection signals and coupled to saidfirst terminals of said first and second deflection yoke windings,respectively, for providing current flow therethrough; means connectedto said rst and second deflection yoke windings for generating atracking voltage which follows the more negative voltage appearing oneither of said windings by a predetermined amount and for applying saidtracking voltage to said first and second transistors; and meansconnected to said first and second transistors for supplying a constantcurrent thereto thereby to minimize energy dissipation therein.

2. The apparatus for magnetically deflecting the electron beam of acathode-ray type tube as defined in claim 1 wherein said means forgenerating a tracking voltage which follows the more negative voltageappearing on either of said windings by a predetermined amount includesa constant voltage network constituting a capacitor and a Zener diodeconnected in parallel.

3. An apparatus for magnetically defiecting the elec tron beam of acathode-ray type tube, said apparatus comprising first and seconddeflection yoke windings each having first and second terminals, saidsecond terminals thereof being returned to a first junction maintainedat ground potential; first and second npn type transistors each havinga. base responsive to push-pull deflection signals, an emitter connectedto a second junction and a collector connected to said first terminalsof said first and second deflection yoke windings, respectively; meansconnected to said second junction for supplying a constant currentthereto; means connected to said first terminals of said first andsecond deflection yoke windings for generating a tracking voltage whichfollows the more negative voltage appearing at either of said firstterminals of said first and second deflection yoke windings and forapplying said tracking voltage t said bases of said first and secondtransistors thereby to minimize energy dissipation therein.

4. An apparatus for magnetically defiecting the electron beam of acathode-ray type tube, said apparatus comprising first and seconddeflection yoke windings each having first and second terminals, saidsecond terminals thereof being returned to a first junction maintainedat ground potential; first and second n-pn type transistors each havinga base responsive to push-pull deflection signals, an emitter connectedto a second junction and a collector connected to said first terminalsof said first and second defiection yoke windings, respectively; meansconnected to said second junction for supplying a constant currentthereto; a third n-p-n type transistor having an emitter, a base and acollector, said Collector being connected to a third junction maintainedat a potential that is positive relative to said reference potential; afirst resistor connected from said third junction to said base of saidthird transistor; a second resistor and a first diode serially connectedfrom said base of said third transistor to said first terminal of saidrst deflection yoke Winding and a third resistor and a second diodeserially connected from said base of said third transistor to said firstterminal of said second deflection yoke winding, said first and second.diodes being poled to allow current fiow away from said base of saidthird transistor; a first capacitor and a Zener diode connected inparallel from said emitter of said third transistor to a fourthjunction; a fourth n-p-n type transistor having an emitter connectedthrough a fourth resistor to a fifth junction maintained at a potentialnegative relative to said reference potential, a collector connecteddirectly `to said fourth junction and a base connected through a fifthresistor to said first junction and through a sixth resistor and asecond capacitor in parallel to said fifth junction; and seventh andeighth resistors connected from said fourth junction to said bases ofsaid first and second transistors, respectiveiy.

5. The apparatus for magnetically defiecting the electron beam of acathode-ray type tube as defined in claim 4 wherein said push-pulldeflection signals are provided by a paraphase amplifier and whichadditionally includes first and second impedance elements interposedbetween said second terminals of said first and second deflection yokewindings, respectively, and said fir-st junction; and means connectedfrom said second terminals of said first and second deiiection yokewinding to said paraphase amplifier for providing feedback thereto.

References Cited in the file of this patent UNITED STATES PATENTS2,629,006 Oliver Feb. 17, 1953 2,762,870 Sziklai et al Sept. 11, 19562,853,650 Close Sept. 23, 1958 2,964,673 Stanley Dec. 13, 1960

1. AN APPARATUS FOR MAGNETICALLY DEFLECTING THE ELECTRON BEAM OF ACATHODE-RAY TYPE TUBE, SAID APPARATUS COMPRISING FIRST AND SECONDDEFLECTION YOKE WINDINGS EACH HAVING FIRST AND SECOND TERMINALS, SAIDSECOND TERMINALS THEREOF BEING RETURNED TO A COMMON JUNCTION MAINTAINEDAT GROUND POTENTIAL; FIRST AND SECOND TRANSISTORS OF LIKE CONDUCTIVITYTYPES RESPONSIVE TO PUSH-PULL DEFLECTION SIGNALS AND COUPLED TO SAIDFIRST TERMINALS OF SAID FIRST AND SECOND DEFLECTION YOKE WINDINGS,RESPECTIVELY, FOR PROVIDING CURRENT FLOW THERETHROUGH; MEANS CONNECTEDTO SAID FIRST AND SECOND DEFLECTION YOKE WINDINGS FOR GENERATING ATRACKING VOLTAGE WHICH FOLLOWS THE MORE NEGATIVE VOLTAGE APPEARING ONEITHER OF SAID WINDINGS BY A PREDETERMINED AMOUNT AND FOR APPLYING SAIDTRACKING VOLTAGE TO SAID FIRST AND SECOND TRANSISTORS; AND MEANSCONNECTED TO SAID FIRST AND SECOND TRANSISTORS FOR SUPPLYING A CONSTANTCURRENT THERETO THEREBY TO MINIMIZE ENERGY DISSIPATION THEREIN.